As device and features size continue to shrink in the semiconductor industry, and also as 3D device structures (e.g., Intel's Tri-Gate transistor architecture) become more prevalent in integrated circuit (IC) design, the capability of depositing thin conformal films (films of material having a uniform thickness relative to the shape of the underlying structure, even if non-planar) will continue to gain importance. Atomic layer deposition (ALD) is a film forming technique which is well-suited to the deposition of conformal films due to the fact that a single cycle of ALD only deposits a single thin layer of material, the thickness being limited by the amount of one or more film precursor reactants which may adsorb onto the substrate surface (i.e., forming an adsorption-limited layer) prior to the film-forming chemical reaction itself. Multiple “ALD cycles” may then be used to build up a film of the desired thickness, and since each layer is thin and conformal, the resulting film substantially conforms to the shape of the underlying device structure.
Silicon nitride (SiN) films are one important variety of dielectric film which may be formed via ALD in the fabrication of modern transistor designs. Due to the role of SiN films in these architectures, it is often desirable for SiN films to have a low wet etch rate. Yet, the formation of such etch-resistant SiN films via ALD processes has been difficult to achieve within typical thermal budget constraints. Hence what is sought are improved methods and apparatus for forming such films.